How Mother's Milk is Made

Linda J. Smith, BSE, FACCE, IBCLC

"Not Enough Milk" is the most common reason for supplementing or discontinuing breastfeeding. Sometimes this is real; other times it is imagined. The progress in understanding milk synthesis comes partly from dairy physiologists (who have a financial interest in knowing exactly how to make lots of milk) and partly from those helping women. Here's a very quick summary of a 2-hour talk I've presented on the subject:

1. Before the 1940's, everyone thought most of the milk was made during the let-down reflex, because it flows faster during let-down. The emphasis was on mothers avoiding "stress," which was thought to inhibit the let-down reflex. (This includes dairy people as well as breastfeeding advocates).

2. In 1944, Peterson showed that milk secretion was continuous but let-down was a different and separate process. Let-down (or MER - milk ejection reflex) squeezes out milk that is ALREADY MADE and stored in the alveolar lumen. It just FLOWS faster - it isn't made any faster during MER.

3. In the 1990's, Peter Hartmann's research in Australia with breastfeeding women corroborated dairy research of Schanbacher and others. He found (actually "is finding" - present tense- this research is ongoing) that the rate of synthesis - how fast the secretory cells pump out milk - was related to the degree of emptiness (or fullness) of the breast. This is autocrine control. As the lumen fills, compounds in the retained milk itself (peptides, fatty acids and possibly other components) signal the cell to SLOW down making more of the stuff. The emptier the breast is, the faster it tries to refill - similar to an automatic ice-maker. (A toilet tank sorta works the same way.) Hartmann says the rate of milk synthesis ranges from 11 to 58 ml/hour/breast, or about 1/3 of an ounce to 2 ounces per breast per hour. Emptier breasts make milk faster than fuller ones.

4. If milk is regularly and thoroughly removed from the breast, milk synthesis keeps chugging along unrestricted. Milk retained in the breast downward-regulates total supply to about 15-20% more than the baby takes on an average. The principle goes like this: if more than 80% of the milk is removed, supply increases to maintain the 80-20 ratio. If less than 80% is removed, supply decreases to maintain the 80-20 ratio. Of course this is an oversimplification of a very complex process, but this principle has held steady as new research emerges.

5. Mom's diet, her fluid intake, and other factors are relatively minor players in this drama. (I make this statement based on my digging into the literature and 27 years working with mothers.) If the "milk removal" piece is in place, moms make plenty of good milk regardless of dietary practices. If the "milk removal" part isn't there, nothing else can make up the difference.

6. The significant inhibiting factors appear to be (1) breast surgery; (2) retained placenta; (3) Sheehan's syndrome or pituitary shock; (4) hormonal contraception. If none of those are factors, it's exceedingly rare than a mom won't make plenty of milk. Rare situations DO exist, however.

7. There were several recent articles in the Journal of Human Lactation on this topic by Daly and Hartmann, and Hartmann's talk from ILCA 1990 is still available on tape. Floyd Schanbacher's talk at ILCA 1996 (which was taped) explained this very expertly.

8. In my practice, the two most common reasons for "not enough" are: (1) the baby isn't at breast enough minutes per day: nursing sessions are ended before the baby lets go, or feeding intervals are stretched out too far between, or something else is given to the baby to "tide them over." OR, (2) the baby is not effectively transferring milk: either because of shallow attachment at breast, or a sucking problem. A good lactation consultant usually can readily fix these problems. My New Years' Wish/plea to all: look at the baby carefully. I don't hesitate to recommend pumps because I see so many babies with poor suck responses at first. The poor suck leaves milk in the breast, which compromises milk supply, resulting in a hungry disorganized baby and no milk. At least with a good pumping routine, we have plenty of mom's milk to work with while we figure out how to help the baby feed better. Supply is usually the easiest part to fix. It's still supply and demand, or "use it or lose it."

POSTSCRIPT: I've received several requests to reprint this Lactnet post "how milk is made." This presents a real dilemma since (1) I want the information and ideas to spread widely, but (2) simply reprinting my post doesn't do the subject justice and may even backfire on the presenter. I didn't mean for this to be a "magic bullet" to hand to others with the admonition "Here, read THIS!!" I wanted it to be a springboard to learning more about the subject, and to serve as a catalyst for your own thoughts on how to better explain this to others. The most important idea I tried to present is "READ the literature" and "do your homework" on this and other subjects pertinent to breastfeeding.

Milk synthesis is a very complex process. People get PhD's studying it and researching the mechanisms involved. I've merely summarized/explained what I've learned from the research, lectures, and published literature in a way that helps me to better understand the issue. When I teach or lecture on this subject, it's a 2-hour talk with 45 overheads, and I'm still gathering material. The questions from the audience/students are often (1) challenging, (2) very sophisticated, (3) and sometimes confrontive. I keep a big folder of my notes, original research articles, page notations from texts, etc. handy to answer questions. So for those who asked: yes, please do print out a personal copy. Yes, please do use the ideas! But No, please do not hand it out to others or re-post it unless you are very secure with the information and ideas yourself.